The present invention relates a method for manufacture of fiber reinforced rod.
The term xe2x80x9crodxe2x80x9d as used herein is intended to include bars and rods which are hollow, that is tubing. The outside surface is preferably but not necessarily of circular cross-section. The rods can be of any length including elements which are relatively short so that they are sometimes referred to as xe2x80x9cboltsxe2x80x9d.
The use of fiber reinforced plastics (FRP) rods in construction, marine, mining and others has been increasing for years. This is because FRP has many benefits, such as non-(chemical or saltwater) corroding, non-metallic (or non-magnetic) and non-conductive, about twice to three times tensile strength and xc2xc weight of steel reinforcing rod, a coefficient of thermal expansion more compatible with concrete or rock than steel rod. Most of the bars are often produced by pultrusion process and have a linear or uniform profile. Conventional pultrusion process involves drawing a bundle of reinforcing material (e.g., fibers or fiber filaments) from a source thereof, wetting the fibers and impregnating them (preferably with a thermosettable polymer resin) by passing the reinforcing material through a resin bath in an open tank, pulling the resin-wetted and impregnated bundle through a shaping die to align the fiber bundle and to manipulate it into the proper cross-sectional configuration, and curing the resin in a mold while maintaining tension on the filaments. Because the fibers progress completely through the pultrusion process without being cut or chopped, the resulting products generally have exceptionally high tensile strength in the longitudinal direction (i.e., in the direction the fiber filaments are pulled). Exemplary pultrusion techniques are described in U.S. Pat. No. 3,793,108 to Goldsworthy; U.S. Pat. No. 4,394,338 to Fuwa; U.S. Pat. No. 4,445,957 to Harvey; and U.S. Pat. No. 5,174,844 to Tong.
FRP uniform profile or linear rods offer several advantages in many industrial applications. The rods are corrosion resistant, and have high tensile strength and weight reduction. In the past, threaded steel rods or bolts had been widely used in engineering practice. However, long-term observations in Sweden of steel bolts grouted with mortar have shown that the quality of the grouting material was insufficient in 50% of the objects and more bolts have suffered from severe corrosion (see reference Hans K. Helfrich). In contrast with the steel bolts, the FRP bolts are corrosion resistant and can be simultaneously used in the temporary support and the final lining, and the construction costs of single lining tunnels with FRP rock bolts are 33% to 50% lower than of tunnels with traditional in-site concrete (see reference Amberg Ingenieurburo AG, Zurich). This FRP rock bolting system is durable and as a part of the final lining supports a structure during its whole life span. Furthermore, due to their seawater corrosion resistance, the FRP bolts and anchors are also proven as good solutions in waterfront (e.g., on-shore or off-shore seawalls) to reinforce the concrete structures. In general the fibreglass rod/bolt is already an important niche, and will be a more important product to the mining and construction industries. The critical needs of these industries are for structural reinforcements that provide long-term reliability that is of cost-effective. The savings in repair and maintenance to these industries will be significant, as the composite rebar will last almost indefinitely.
The mining industry requires composite rods for mining shafts or tunnel roof bolts. These rods are usually carried by hand and installed overhead in mining tunnel, so there is a benefit that the fibreglass rod is xc2xc the weight and twice the strength of steel rebar which are widely used currently. Fibreglass rod also does not damage the mining equipment. In construction industries, such as bridges, roads, seawall and building structures, reinforcements of the steel rebar have been widely used and the most of steel rebars have been corroded after a few years of service life. Typically, the structures with the steel rebars are often torn down after a period of time. Therefore, the use of the corrosion resistant composite rebars have been increased for construction industries in recent years.
Non-uniform profile or non linear threaded rods are also required in many industrial applications. For example, threaded FRP rods and associated nuts have been used as rock bolting system in mining industries (e.g., for tunnel roof bolts), as threaded reinforcing rebar structures in construction industries (e.g., in bridge construction), as well as seawall bolting system in marine structures.
The structures of the threaded composite rods from existing manufacturing technology consist of two styles:
(1) Pultruded rod with machined threads in outside surface, and
(2) Pultruded rod has a core of fiber rovings with plastic materials molded outside the core to form threads.
In style (1), the problem of machining composite rebar surface after it is fully cured is that the fibers in a depth of surface are cut into segments. The benefit of high tensile strength of the fibers are lost when they are cut into short lengths. The strength of the threads now rely on the shear strength of the cured resin which is much less than that of the fibers. Thus, the rebar could not be used under tension since the threads of the rebar will shear away from the core. The rebar uses a specially designed nut that compresses against the rebar to give it holding strength when a load is placed on the rebar. The nut of threaded onto the rebar has just enough resistance to take up any slack between the nut and the thread surface. Therefore the nut is used without pre-tension.
In style (2), the rebar has a core of fiberglass rovings and a plastics molded threads surface. This rebar is only capable of withstanding a small amount of longitudinal loads. This is because the threads formed by the molded plastics lack the fiberglass reinforcements for having the longitudinal strength. Other rebars, such as those shown in a brochure by Marshall Industries Composites Inc C-BAR 1996, are a combination of a fiber-reinforced polyester core and a urethane-modified vinyl ester outer skin, which do not include the thread features in rebar surface.
There is therefore a need in mining, construction and other industries for composite rod and nut fastening system that the rod and nut have a fully threaded feature without the disadvantages of the style (1) and (2) described in the paragraph above.
In view of the foregoing, it is one object of the present invention to provide a fully threaded glass-fiber reinforced composite rod, and associated mechanical fastening system.
It is also an object of the present invention to provide a method for manufacturing a molded rod by pressing and squeezing the resin out of the impregnated fibers to the mold internal surfaces.
According to the invention there is provided a method for forming a threaded rod comprising:
providing a longitudinally continuous fibrous structure formed of a plurality of fibers;
the fibrous structure including longitudinally extending continuous fibers;
impregnating the fibrous structure with a settable resin;
collating the impregnated fibrous structure including the longitudinally extending continuous fibers into an elongate continuous rod in which the resin throughout the rod is an un-set condition;
providing a generally cylindrical die having a plurality of die parts for surrounding a portion of the rod and for extending along a part of the length of the rod, which die parts can be opened in a direction transverse to the length of the rod to receive the rod and clamped together to form a hollow die interior defining a generally cylindrical shape with a continuous helical thread therealong;
in a compression step, closing the die parts into a closed position onto the portion of the length of the impregnated fibrous structure while the resin remains in the un-set condition so as to apply a compressive force from the die parts onto the rod in a direction transverse to the length to cause the portion of the fibrous structure to conform to the shape of the hollow interior and thus to mold on the fibrous structure a helical thread which is substantially continuous along the portion and which has a helical thread root having a minimum diameter at a core of the fibrous and a helical thread crest having a maximum diameter;
and causing the compressive force within the hollow interior so as to distort some of the longitudinally extending continuous fibers of the portion of the rod such that a portion of the distorted fibers lies inwardly of the root and a portion extends into the thread toward the crest such that the thread is reinforced by the longitudinally extending continuous fibers which extend from the thread into the core;
heating the die parts to set the resin in the portion;
moving the die parts from the closed position to a release position;
with the die parts in the release position, pulling the rod with the resin set therein longitudinally so as to move the portion of the rod with the molded thread thereon longitudinally out of the die and to move a further portion of the rod with the resin in an un-set condition impregnated therein into the die;
and repeating the compression step on the further portion.
Where the above definition refers to movement of the die parts, it will be appreciated that one or both part may be moveable or one may be fixed to obtain the required relative movement between them as set forth.
If it is required to be hollow, there may be provided a mandrel inside the die to form a hollow interior of the rod or there may be provided a tubing core inside the rod.
Preferably the die parts include a first die part and a second die part, each of the die parts having a part cylindrical surface forming a part of the hollow die interior defining the generally cylindrical shape such that, when the die parts are in closed position, the part cylindrical surfaces are coaxial to form the hollow die interior; wherein the first die part and the second die part each include parallel mating surfaces on each side of the part cylindrical surface; and wherein the first and second die parts are moved in the compression step from the release position in which the mating surfaces of the first die part are spaced from the mating surfaces of the second die part in a first direction transverse to the mating surfaces to bring the mating surfaces into contact together with the part cylindrical surfaces axially offset and in a second direction parallel to the mating surfaces to bring the part cylindrical surfaces into the closed co-axial position to form the hollow die interior into the generally cylindrical shape.
Preferably the mating surfaces of the first and second die parts on one side of the part cylindrical surfaces lie in a first plane which is parallel to and spaced from a second plane containing the mating surfaces of the first and second die parts on an opposed side of the part cylindrical surfaces.
Preferably the first and second die parts are moved from the closed position to the release position in a direction which is inclined to a right angle to the mating surfaces.
Preferably the first and second die parts are moved from the closed position to the release position in a direction which is substantially at right angles to a plane intersecting edges of the part cylindrical surfaces.
Preferably movement of the first and second die parts in the second direction, with the mating surfaces in contact, causes un-set resin to be swept from the mating surfaces into the hollow die interior.
Preferably the first and second die parts move from the closed position to the release position and back to the closed position in a generally triangular path.
Preferably the die parts include a first die part and a second die part, each of the die parts having a part cylindrical surface forming a part of the hollow die interior defining the generally cylindrical shape such that, when the die parts are in closed position, the part cylindrical surfaces are coaxial to form the hollow die interior; the first die part and the second die part each include parallel mating surfaces on each side of the part cylindrical surface; and the mating surfaces of the first and second die parts on one side of the part cylindrical surfaces lie in a first plane which is parallel to and spaced from a second plane containing the mating surfaces of the first and second die parts on an opposed side of the part cylindrical surfaces.
Preferably the first and second die parts are moved from the closed position to the release position in a direction which is inclined to a right angle to the mating surfaces.
Preferably the first and second die parts are moved from the closed position to the release position in a direction which is substantially at right angles to a plane intersecting edges of the part cylindrical surfaces.
According to a second aspect of the invention there is provided a method for forming a molded rod comprising:
providing a longitudinally continuous fibrous structure formed of a plurality of fibers;
the fibrous structure including longitudinally extending continuous fibers;
impregnating the fibrous structure with a settable resin;
collating the impregnated fibrous structure including the longitudinally extending continuous fibers into an elongate continuous rod in which the resin throughout the rod is an un-set condition;
providing a generally cylindrical die having a plurality of die parts for surrounding a portion of the rod and for extending along a part of the length of the rod, which die parts can be opened in a direction transverse to the length of the rod to receive the rod and clamped together to form a hollow die interior defining a generally cylindrical shape;
in a compression step, closing the die parts into a closed position onto the portion of the length of the impregnated fibrous structure while the resin remains in the un-set condition so as to apply a compressive force from the die parts onto the rod in a direction transverse to the length to cause the portion of the fibrous structure to conform to the shape of the hollow interior;
heating the die parts to set the resin in the portion;
and moving the die parts from the closed position to a release position;
wherein the die parts include a first die part and a second die part, each of the die parts having a part cylindrical surface forming a part of the hollow die interior defining the generally cylindrical shape such that, when the die parts are in closed position, the part cylindrical surfaces are coaxial to form the hollow die interior;
wherein the first die part and the second die part each include parallel mating surfaces on each side of the part cylindrical surface;
and wherein the first and second die parts are moved in the compression step from the release position in which the mating surfaces of the first die part are spaced from the mating surfaces of the second die part in a first direction transverse to the mating surfaces to bring the mating surfaces into contact together with the part cylindrical surfaces axially offset and in a second direction parallel to the mating surfaces to bring the part cylindrical surfaces into the closed co-axial position to form the hollow die interior into the generally cylindrical shape.
According to a third aspect of the invention there is provided a method for forming a molded rod comprising:
providing a longitudinally continuous fibrous structure formed of a plurality of fibers;
the fibrous structure including longitudinally extending continuous fibers;
impregnating the fibrous structure with a settable resin;
collating the impregnated fibrous structure including the longitudinally extending continuous fibers into an elongate continuous rod in which the resin throughout the rod is an un-set condition;
providing a generally cylindrical die having a plurality of die parts for surrounding a portion of the rod and for extending along a part of the length of the rod, which die parts can be opened in a direction transverse to the length of the rod to receive the rod and clamped together to form a hollow die interior defining a generally cylindrical shape;
in a compression step, closing the die parts into a closed position onto the portion of the length of the impregnated fibrous structure while the resin remains in the un-set condition so as to apply a compressive force from the die parts onto the rod in a direction transverse to the length to cause the portion of the fibrous structure to conform to the shape of the hollow interior;
heating the die parts to set the resin in the portion;
and moving the die parts from the closed position to a release position;
wherein the die parts include a first die part and a second die part, each of the die parts having a part cylindrical surface forming a part of the hollow die interior defining the generally cylindrical shape such that, when the die parts are in closed position, the part cylindrical surfaces are coaxial to form the hollow die interior;
wherein the first die part and the second die part each include parallel mating surfaces on each side of the part cylindrical surface;
and wherein the mating surfaces of the first and second die parts on one side of the part cylindrical surfaces lie in a first plane which is parallel to and spaced from a second plane containing the mating surfaces of the first and second die parts on an opposed side of the part cylindrical surfaces.
If threaded, the thread may extend along the full length of the rod or thread portions may be separated each from the next by a short length where the rod is not threaded or smooth. Such smooth portions are provided between each molded section and the next to avoid misalignment of the threads formed by the molds which could cause damage to the molds. Molding techniques which avoid this alignment problem as described hereinafter can provide a method for generating a continuous thread.
The present invention thus may provide a fully threaded FRP rod for use with a mechanical fastening systems, a forming process of the threaded composite bars, and the apparatus for making such the threaded rods. The threaded rods can operate with a nut or coupling to be screwed onto the ends of the rod. The rods can be tensioned with the nut or jointed together with 45, 90 , etc., elbow couplings to allow the rod to make turns or bends. The threaded rod can also be fastened together to make various patterns for reinforced concrete. The threaded rod can also be jointed together with FRP or plastic nut connectors to extend to any length of the rod in sites to avoid transportation problems. The threads on the rod are not only used for screwing on nuts and adapters, but they also provide an excellent anchoring system when the rod is glued or grouted into rock or concrete. The threads make it very difficult for the rod to be pulled out of the rock or concrete cement.